In radio frequency (RF) wireless communication systems, a power amplifier is a component having high impact on power consumption. Therefore, a high efficiency of the power amplifier may be beneficial to conserving energy and increasing battery lifetime.
Constant envelope modulations of RF signals allow power amplifiers to operate at or near saturation levels. This implies that the power amplifiers may be efficiently used, as the modulation scheme may be provided with a low peak-to-average power ratio.
The signals transmitted by radio transmitters should meet electromagnetic interference (EMI) regulations. EMI regulations may differ between different countries, but are used for ensuring that radio signals do not interfere with each other and that transmitters transmitting in authorized bands do not interfere with signals outside the bands for which transmission is authorized.
It would be desirable to provide a RF transmitter having close control of transmitted frequencies and power to meet EMI regulations and, possibly, to adapt to different EMI regulations in different countries, while minimizing energy consumption.
In Sang-Min Yoo et al., “A Switched-Capacitor RF Power Amplifier,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, vol. 46, no. 12, pp. 2977-87 (December 2011), a switched-capacitor power amplifier is shown operating on an envelope of a non-constant envelope modulated signal in order to amplify the signal efficiently.